The invention relates to a pressure electrolyser, and a process for switching off a pressure electrolyser.
Pressure electrolysers which comprise a pressure reservoir and an electrolytic cell block which is positioned in the pressure reservoir and contains a number of electrolytic cells combined in the form of a stack are known for the electrolytic splitting of water into hydrogen and oxygen. The electrolytic cells contain anodes and cathodes, and an electrolyte circulatory system is provided for supplying electrolyte to the anodes and cathodes. An oxygen separator serves to separate the gaseous oxygen formed during the operation of the pressure electrolyser and a hydrogen separator serves to separate the gaseous hydrogen formed during the operation of the pressure electrolyser. In order to inert the pressure electrolyser when it is switched off a store of an inert gas, in particular nitrogen, is provided.
A pressure electrolyser of traditional type is known from DE 25 48 699 C3, for example.
A vital safety factor in pressure electrolysers of the type specified lies in their capacity to be inerted quickly, reliably and fully, i.e. in the removal of the hydrogen from the pressure reservoir and from the hydrogen separator, such that the residual hydrogen content is well below the lower explosion limit of 4% by vol.
Traditionally, large quantities of inert gas, typically nitrogen, are held ready for inerting, it being used to rinse the hydrogen out of the hydrogen separator when the electrolyser is switched off, in the event of an emergency shutdown, for example. To this end the pressure in the pressure electrolyser may either be maintained or reduced to ambient pressure in the course of rinsing with the inert gas. In any event, due to the mixing of the gases a, multiple of the gas volume of the hydrogen separator must be held ready in the form of inert gas. Since, due to the evolution of hydrogen or oxygen in hidden caverns, decompressing the electrolyser at speed typically causes damage to the seals and structural components of the cells and means that the subsequent restarting of the unpressurised plant is associated with considerable energy expenditure, the electrolyser should, where possible, only be decompressed in three, genuinely unavoidable emergency scenarios: an electrolyte leak, a product gas leak or a critical impurity in the product gas. In all other cases pressure should be maintained when the electrolyser is switched off.